1. Field of the Invention
This invention relates generally to a vibration isolator, and more particularly to a vibration isolator that prevents an image blur due to a vibration of a TV camera by moving a correcting lens.
2. Description of Related Art
Conventionally, a vibration isolator for a TV camera supports a correcting lens that is movable within a plane that is perpendicular to an optical axis in a lens barrel. When the camera is vibrated, actuators move the correcting lens in such a direction as to cancel the vibration to prevent an image blur. The vibration applied to the camera is determined by vibration speed sensors (angular speed sensors or speed sensors) provided in a camera body or the lens barrel.
Japanese Patent Provisional Publication No. 6-118469 discloses a method of appropriately eliminating an error of correction for drift (change of output from a sensor as time passes) of a vibration speed sensor that determines a vibration applied to a camera.
Japanese Patent No. 2918537 discloses a vibration isolator that twice integrates a signal outputted from an acceleration sensor of a camera with an integrator and moves a correcting lens in a direction that is opposite from that of the movement (vibration) of the camera according to the output from the integrator with a driving device (voice coil).
In the vibration isolator, when the vibration isolation is OFF, no signal is inputted to the driving device and the correcting lens is kept at a specific position. When the vibration isolation is turned ON and a signal starts being inputted to the driving device according to the vibration, the signal discontinuously changes. As a result, the correcting lens suddenly moves and an image blur occurs. To address this problem, the signal has a predetermined value (zero) for keeping the correcting lens at the specific position when the vibration isolation is turned ON, and the value is changed according to the output signal from the integrator. In this case, a differential amplifier is connected between the integrator and the driving device, and the output signal from the integrator is inputted to one input terminal of the differential amplifier, and the output signal from the integrator is inputted to the other input terminal through a sampling/holding circuit. When the vibration isolation is OFF, the sampling/holding circuit samples the output signal from the integrator to make the value of the signal outputted from the differential amplifier to the driving device zero in order to hold the correcting at the specific position. When the vibration isolation is ON, the sampling/holding circuit holds the output signal from the integrator to set the output signal from the integrator as a reference, and the change of the output signal from the integrator with respect to the reference is outputted from the differential amplifier to the driving device. Thus, even when the vibration isolation is turned ON, the signal inputted to the driving signal is not discontinuous in order to prevent an image gap.
Japanese Patent Provisional Publication No. 11-284900, which corresponds to pending U.S. patent application Ser. No. 09/277,772 assigned to the assignee of the present application, discloses a vibration isolator that is provided on a lens supporter for attaching a lens device to a camera body. In the vibration isolator, a vibration determining device (an angular speed sensor or an acceleration sensor) is directly arranged in the camera body or a lens barrel.
In the method disclosed in Japanese Patent Provisional Publication No. 6-118469, the vibration speed sensor determines the vibration applied to the camera, and the position of the correcting lens for preventing the image blur is found according to the output from the sensor. However, there is a question on how the correcting lens is controlled with the center of the operation range at the origin.
The position of the correcting lens for preventing the image blur is the integrated value of the output signal from the sensor, and the position is controlled so that the correcting lens is at the origin when the integrated value is zero. However, the integrated value varies according to the starting point of the integration, and when the integrated value is zero varies according to the starting point. As a result, the operation range of the correcting lens changes according to the starting point. Thus, the center of the operation range is not always the origin. The center can be largely displaced from the origin, and the operation range is restricted by a mechanical end, and therefore the vibration isolator's full ability is not realized. The center of the operating range is preferably the origin so that the vibration isolator's full ability is realized. However, Japanese Patent Provisional Publication No. 6-118469 does not explain how the correcting lens is controlled with the center of the operation range at the origin.
If the output signal from the sensor includes noise components or drift components, the components are accumulated in the integrated value of the output signal. In this case, even if the center of the operation range is the origin at the beginning, the center is gradually displaced from the origin and the vibration isolator's full ability is not realized.
In the vibration isolator disclosed in Japanese Patent No. 2918537, when the vibration isolation is ON, the output signal from the integrator is set as the reference, and the change of the output signal from the integrator with respect to the reference is outputted from the differential amplifier to the driving device in order to prevent the image gap. Thus, the oscillation center of the correcting lens is displaced from the origin (center of the range in which the correcting lens can move). The oscillation range is restricted within the range in which the correcting lens can move. If the center of the operation range is displaced from the origin, the maximum oscillation gets smaller, and the vibration isolator can not appropriately prevent the image blur when the vibration of the camera is large. In short, the vibration isolation is deteriorated to prevent the image gap.
If the vibration isolation is started when a predetermined switch (a shutter release button in Japanese Patent No. 2918537) is operated, the vibration isolation is unstable because of a vibration caused by the operation of the switch, and it further blurs the image.
The above problem is caused because the vibration isolator tries to completely prevent the image blur when the switch is operated. However, the image blur does not have to be prevented when the switch is operated in an apparatus such as the lens device for the TV camera and a still camera.
In the vibration isolator disclosed in Japanese Patent Provisional Publication No. 11-284900, the vibration determining device is directly arranged in the camera body or the like. The vibration determining device determines a vibration caused by the movement of the correcting lens, and the vibration caused by the movement of the correcting lens does not cause the image blur. Thus, the vibration isolation is deteriorated.